Moon-Phase Indication and Moon Phases
Indication with the number of days since the last new moon. In the synodical month, one lunation, the time interval from new moon to new moon, or moon-phase, is exactly 29 days, 12 hours and 44 minutes. Such an indication usually consists of a disc with 59 teeth on its rim, and with two opposite full moons on its upper surface. Driven by the hour wheel, it turns once on its axis in two lunations. Its position is shown through a window in the dial. This cutout is sometimes complemented by a graduated scale of 29.5 days. Depending on their design, watches with moon-age indication can err from one minute to about eight hours in a year.
The moon goes through its phases (new moon-first quarter-full moon-last quarter-new moon), which depend on the positions of the sun, moon and earth, in a lunation of approximately 29.5 days.